WHERE DID YOU GO WRONG - ERRORS, PARTIAL ERRORS, AND THE NATURE OF HUMAN INFORMATION-PROCESSING

Human performance is seldom perfect, and even when an overt response i s correct it may be accompanied by partial-error activity that does no t achieve the level of a complete incorrect response. Partial errors c an be detected in measures of the lateralized readiness potential, of the electromyogram, and of response force. Correct responses accompani ed by partial errors tend to have slower reaction times than ''clean'' correct responses (because of response competition), and condition di fferences in reaction time can, on some occasions, be explained in ter ms of differences in the incidence of partial errors. In two-choice re action time tasks, partial errors are more frequent when the imperativ e stimulus contains information that favors both responses, than when it contains information that favors only one response. The non-random nature of partial errors supports the inference that partial informati on about the stimulus is used to guide responses. A similar inference is supported by the observation that, in hybrid choice Go/No-go tasks, the kinds of partial errors that follow a No-go stimulus represent ac tivation of the response that would have been correct had the stimulus been a Go stimulus. Finally, we note that the human processing system is capable of monitoring its own behavior and of initiating remedial actions if necessary. The activity of an error-detection system, as re vealed by measures of the error-related negativity, is related to the degree to which responses are slowed after errors.